1. Field of the Invention
The present invention relates to a plastic catheter system useful for the accurate insertion of catheters for radiotherapy by the afterloading method.
2. Discussion of the Background
Radiotherapy is of proven use for the treatment of tumors. The recognized method for radiation treatment in body cavities, such as in the throat, bowel or vaginal region, and in regions of the body opened surgically, is brachytherapy, in which one or more radiation sources is brought, controlled by an afterloading device, in a precise and metered manner to the site of treatment in the body. The radiation source is then moved to provide a previously calculated isodose contour, as described in D. E. Wazer, R. Schmidt-Ullrich, W. Chasin, A. Wu, M. Buscher, Am. J. Otolaryngology 10 (3), (1989), 173 and R. Stepan, P. Lukas, U. Fink, P. Kneschaurek, Ir. Siewert, M. Molis, "Intraoperative Radiotherapy with High Dose Afterloading (Flabs Method) in Colorectal Carcinoma", in F. W. Schildberg, N. Willich, H. -J. Kramling (Editors) "Intraoperative Radiation Therapy", Proceedings 4th International Symposium IORT, Munich 1992, Verlag Die Blaue Eule, Essen.
In order to avoid harming the patient and to guarantee the requirements for accurate irradiation, the catheters must be accurately positioned and, in addition, fixed on or in the body. Only when this is ensured can programming of the required isodose contour take place and pre-planned irradiation be guaranteed.
It must also be ensured that the mobility of the radiation sources guided by the catheters is not impaired either by kinks, constrictions or excessively severe radii of curvature of the catheters. If the radiation source becomes trapped, there may be considerable overdosage, with serious risk of harm to the patient. The emergency measures which are then necessary are those associated with unavoidable exposure of staff to radiation (Isabel Gosh, Sicherheitstechnisch bedeutsame Ereignisse an Afterloadinganlagen: Untersuchungen zur Strahlenexposition, Folgerungen zur Sicherheit von Personal und Patient [Events with relevance to safety in afterloading systems: investigations on radiation exposure, consequences for safety of staff and patient] Diplomarbeit Berufsakademie, Karlsruhe, 1991).
In the event of repeated radiation treatments, where a reduced radiation dose is given in each subsequent treatment, secure fixation of the catheters at the site of treatment over a lengthy period is particularly important. Moreover, accurate catheter fixation is necessary so that external and convenient preparation of patients who live some distance away from the radiotherapy centers is possible. In addition, this makes it possible for a much larger number of patients to be referred for radiotherapy treatment than previously possible.
The conventional practice for producing fixed catheter sets is to cut rubber-like standard flat blocks (1 to 3 cm high, area: 30.times.30 cm.sup.2, available from Quandt Medizintechnik, Hamburg, or Mick RadioNuclear Instruments Inc., Bronx, N.Y., for example) to size and then to bore through by hand using a hollow needle in order to fit the catheters therein. These operations are time-consuming, tie up staff and result in inaccurate embedding of the catheters. For example, as the length of the needle increases, the friction on the outer wall of the needle increases, the material of the flat block deforms, and the pierced channels are no longer parallel.
In addition, these blocks containing the catheters, so-called "flabs" in the industry, cannot be securely fixed to the intended site of administration. Tears occur in the holes pierced by the fixing threads and thus the flab becomes displaced or entirely detached. This results in the catheters changing position overall or with respect to one another and the irradiation fails. It is then necessary to carry out a new localization to establish the exact displacement of the catheters. Reoperation is then often necessary, with all the additional risks associated therewith. By contrast, if the catheter fixation can be made secure, some of the patients could also be looked after at their local hospital between irradiation treatments, with a concurrent reduction in costs.
Cylindrical plastic catheter systems are likewise unavailable. Recourse is made to plastic parts with self-drilled holes, as described in the publication by D. E. Wazer et al., cited above, page 177. In the throat, recourse is made to fixation of individual catheters which are equipped with anchors and are sutured in a manner that is time-consuming and considerably stressful for the patient, as described in P. C. Levendag, L. L. Visch, N. Doiver, The Journal of Prosthetic Dentistry, 63 (6), (1990), p. 665.
U.S. Pat. No. 4,963,128 discloses a soft flab equipped with catheters, but it does not yet fully meet practical requirements. The radii of curvature of the outer catheters are small and endanger the mobility of the sources. The loops for fixing the so-called flab are readily torn and often cannot be used fully for fixation because they may be located also in regions where suturing is impossible. The extremely soft material of the flab also does not permit fundamentally secure fixation via the four loops. Furthermore, because of the geometric differences of the areas to be treated, it is necessary to store, at great cost, many different-sized flabs equipped with catheters in this way.
The flabs of the prior art can be used only for treatment points which are extensively flat or have only moderate curvature. Flabs of this design are in principle unsuitable for narrower body cavities or highly curved body and tissue surfaces.